Various types of protocols have been used to transmit information within Orthogonal Frequency Division Modulation (OFDM) systems. For example, Institute of Electrical and Electronic Engineers (IEEE) 802.11 standard protocols have sometimes been used to facilitate the transmission of OFDM symbols in these networks. In these systems, the OFDM symbols include a plurality of subcarriers and groups of symbols can be transmitted together with a preamble in the form of a frame or packet.
As information is transmitted, several types of noise or interference can occur within OFDM systems. For example, intersymbol interference occurs in a given subcarrier of the current OFDM symbol and this interference is attributable to transmissions made in the same subcarrier of some other OFDM symbol. In addition, inter-tone interference also occurs and is caused by other tones in the current or other OFDM symbols. Different metrics can be used to measure and compare the amount of interference in the system or within a current transmission. For example, one measure of the interference in a system is the Signal/Interference (S/I) ratio.
Interference cancellation has not been implemented in typical previous OFDM systems. As a result, the S/I ratio in these systems is limited. When the S/I ratio is limited, the use of higher data rates (such as those used in 16 and 64 Quadrature Amplitude Modulation (QAM) systems) is essentially impossible to achieve. In addition, the maximum S/I limitation desenses the receiver so that the range of communication links in the system is reduced. As a result of these problems, the quality of communications made in previous OFDM systems has often become degraded, and user satisfaction with these systems has suffered.